Levels Of Photosynthetic Pigments Research Articles

Structural Adaptation and Antioxidant Response of Guarianthe bowringiana (O’Brien) Dressler & W. E. Higgins (Orchidaceae Juss.) Seedlings During Ex Vitro Acclimatization

AbstractGuarianthe bowringianais one of the oldest samples cultivated at NBG’s orchid unit glasshouses since 1970s. An efficient protocol for asymbiotic in vitro seed germination ofG. bowringianahas previously been established. Given that acclimatization is a crucial step in micropropagation, this study assesses the structural adaptation and antioxidant response ofG. bowringianaseedlings during ex vitro acclimatization to ex vitro conditions.The leaf surface micromorphology of theG. bowringianajuvenile plants propagated in vitro from seeds as well as the leaves of adult plants cultivated in glasshouse were analyzed using scanning electron microscopy. The levels of lipid peroxidation (TBARS level), superoxide dismutase (SOD) activity, and the photosynthetic activity were monitored for seven days from the transfer of seedlings from the in vitro cultivation vessels as they are markers indicating the response of the leaves of in vitro propagatedG. bowringianaplants to oxidative stress during the early stages of acclimatization to ex vitro conditions. During the initial 2 days of the monitored acclimatization period (0–7 days), the level of photosynthetic pigments (chlorophylla,b, and carotenoid content) increased, followed by an insignificant increase during the successive period (by the seventh day) of acclimatization. At the same time, the level of the tested antioxidant enzyme (SOD) exhibited an increasing trend throughout the acclimatization period. The SOD activities in the leaves ofG. bowringianaseedlings were significantly affected when they were transferred from in vitro to ex vitro conditions due to drought stress.Thus, it was revealed that in the early stages of acclimatizing to the altered environments,G. bowringianaseedlings exhibited a rapid increase in photosynthetic pigments, superoxide dismutase activity, and lipid peroxidation levels after being transferred to ex vitro conditions.Comparison of the leaf micromorphologies ofG. bowringianaplants grown under in vitro and those grown under ex vitro conditions revealed that leaf development had undergone significant changes during acclimatization to the altered conditions. In vitro to ex vitro transfer leads to a transient decrease in photosynthetic parameters.

Daily dynamics of intermediate metabolite profiles lead to time-dependent phenylethanoid glycosides production in Scrophularia striata during the day/night cycle.

Phenylethanoid glycosides (PhGs) are important medicinal compounds found in Scrophularia striata, one of the plant species native to Iran. Since almost all aspects of plant life are controlled by night/light cycle, studying its relationship to valuable plant metabolites production will help us to determine the right time for their extraction. Therefore, the aim of this investigation is to figure out whether the diel light oscillations control PhGs production and how it relates to daily changes in upstream metabolic reactions and circadian clock in S. striata. For this, daily rhythms of metabolic pathways were examined every 4h during a day/night cycle in 3 groups of control (16h light/8h dark), continuous light and darkness. The results showed that acteoside and echinacoside levels in each group peaked during the night and day, respectively. Thus, the PhGs production follows a rhythmic behavior in S. striata, which is probably controlled by circadian clock. Also, the levels of photosynthetic pigments, carbohydrates, amino acids, phenolic acids, phytohormones and phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) enzyme activities varied diel in a similar or different way among study groups. The observations revealed that light/dark cycle controls the carbon and energy flow from light reception to the production and consumption of starch, biosynthesis of phenylalanine, tyrosine, cinnamic acid and coumaric acid, activation of hormonal signaling pathways and enzymes involved in phenylpropanoid pathway. Overall, it can be concluded that PhGs accumulation time-dependent patterns is likely due to daily fluctuations in upstream metabolic reactions induced by light/dark cycle.

Phthalanilic Acid with Biostimulatory Functions Affects Photosynthetic and Antioxidant Capacity and Improves Fruit Quality and Yield in Cowpea (Vigna unguiculata (L.) Walp.)

The widespread application of biostimulants with a growing trend represents sustainable practices aimed at improving growth and yield and alleviating stresses in green agricultural system. Phthalanilic acid (PPA), with biostimulatory functions, has been increasingly applied to fruit and vegetable production. However, its specific biostimulatory effects on growth and development of cowpea (Vigna unguiculata) plants is still unclear. In this study, the regulatory function of foliar spraying PPA at the flowering timing in morphometric (length, width, single pod weight and yield), physiological (relative electrical conductivity), and biochemical (antioxidant enzymes activity, photosynthetic pigment, malondialdehyde, vitamin C, soluble protein, and soluble sugar content) parameters of cowpea plants were investigated. In general, PPA treatments exhibited higher antioxidant enzymes activities (with an increase of 11.89–51.62% in POD), lower relative conductivity (with a decrease of 22.66–62.18%), increased photosynthetic pigment levels and amounts of free proline (with an increase of 24.62–90.52%), and decreased malondialdehyde. Furthermore, the length, width and weight of single pod, podding rate (with an increase of 19.64%), vitamin C, soluble protein (with an increase of 18.75%), and soluble sugar content were increased by 200 mg·L−1 PPA. These data, together with an increased yield of 15.89%, suggest that PPA positively regulates the growth and development, improving fruit quality and yield, especially at 200 mg·L−1. This study indicates that PPA has biostimulatory effects in cowpea production and shows application prospect in field cultivation.

Epiphytic PGPB Bacillus megaterium AFI1 and Paenibacillus nicotianae AFI2 Improve Wheat Growth and Antioxidant Status under Ni Stress.

The present study demonstrates the Ni toxicity-ameliorating and growth-promoting abilities of two different bacterial isolates when applied to wheat (Triticum aestivum L.) as the host plant. Two bacterial strains tolerant to Ni stress were isolated from wheat seeds and selected based on their ability to improve the germination of wheat plants; they were identified as Bacillus megaterium AFI1 and Paenibacillus nicotianae AFI2. The protective effects of these epiphytic bacteria against Ni stress were studied in model experiments with two wheat cultivars: Ni stress-tolerant Leningradskaya 6 and susceptible Chinese spring. When these isolates were used as the inoculants applied to Ni-treated wheat plants, the growth parameters and the levels of photosynthetic pigments of the two wheat cultivars both under normal and Ni-stress conditions were increased, though B. megaterium AFI1 had a more pronounced ameliorative effect on the Ni contents in plant tissues due to its synthesis of siderophores. Over the 10 days of Ni exposure, the plant growth promotion bacteria (PGPB) significantly reduced the lipid peroxidation (LPO), ascorbate peroxidase (APX), superoxide dismutase (SOD) activities and proline content in the leaves of both wheat cultivars. The PGPB also increased peroxidase (POX) activity and the levels of chlorophyll a, chlorophyll b, and carotenoids in the wheat leaves. It was concluded that B. megaterium AFI1 is an ideal candidate for bioremediation and wheat growth promotion against Ni-induced oxidative stress, as it increases photosynthetic pigment contents, induces the antioxidant defense system, and lowers Ni metal uptake.

Disruption of Hydrogen Gas Synthesis Enhances the Cellular Levels of NAD(P)H, Glycogen, Poly(3-hydroxybutyrate) and Photosynthetic Pigments Under Specific Nutrient Condition(s) in Cyanobacterium Synechocystis sp. PCC 6803

In photoautotrophic Synechocystis sp. PCC 6803, NADPH is generated from photosynthesis and utilized in various metabolism, including the biosynthesis of glyceraldehyde 3-phosphate (the upstream substrate for carbon metabolism), poly(3-hydroxybutyrate) (PHB), photosynthetic pigments, and hydrogen gas (H2). Redirecting NADPH flow from one biosynthesis pathway to another has yet to be studied. Synechocystis's H2 synthesis, one of the pathways consuming NAD(P)H, was disrupted by the inactivation of hoxY and hoxH genes encoding the two catalytic subunits of hydrogenase. Such inactivation with a complete disruption of H2 synthesis led to 1.4-, 1.9-, and 2.1-fold increased cellular NAD(P)H levels when cells were cultured in normal medium (BG11), the medium without nitrate (-N), and the medium without phosphate (-P), respectively. After 49-52 d of cultivation in BG11 (when the nitrogen source in the media was depleted), the cells with disrupted H2 synthesis had 1.3-fold increased glycogen level compared to wild type of 83-85% (w/w dry weight), the highest level reported for cyanobacterial glycogen. The increased glycogen content observed by transmission electron microscopy was correlated with the increased levels of glucose 6-phosphate and glucose 1-phosphate, the two substrates in glycogen synthesis. Disrupted H2 synthesis also enhanced PHB accumulation up to 1.4-fold under -P and 1.6-fold under -N and increased levels of photosynthetic pigments (chlorophyll a, phycocyanin, and allophycocyanin) by 1.3- to 1.5-fold under BG11. Thus, disrupted H2 synthesis increased levels of NAD(P)H, which may be utilized for the biosynthesis of glycogen, PHB, and pigments. This strategy might be applicable for enhancing other biosynthetic pathways that utilize NAD(P)H.

CO2 enrichment alters morphophysiology and improves growth and acclimatization in Etlingera Elatior (Jack) R.M. Smith micropropagated plants

Conventional in vitro propagation may affect normal morphophysiological characteristics and survival during the acclimatization of commercial plants, such as Etlingera Elatior (Jack) R.M. Smith. CO2 enrichment, gas-permeable membranes, and reduced carbohydrate concentration in culture media can be used to mitigate these effects. Here, we aimed to determine the impact of photomixotrophic and photoautotrophic growth on morphophysiological responses of E. elatior and its survival during ex vitro acclimatization. In vitro-established plants were placed in flasks containing semisolid MS medium with 0.54 µM α-naphthalene acetic acid and sucrose (0 or 15 g L−1). The flasks were sealed with lids with or without orifices covered by gas-permeable membranes and kept for 45 days under forced-air ventilation (360 or 1000 µmol−1 CO2). Growth variables, anatomical and physiological characteristics, and survival rate were evaluated. Overall, 1000 µmol mol−1 CO2, gas-permeable membranes, and 15 g L−1 sucrose resulted in plants with higher fresh and dry mass, higher level of photosynthetic pigments, as well as more developed secondary ribs in the leaves, prominent midribs, highly organized and differentiated chlorenchyma cells (palisade and spongy parenchyma), more developed vascular bundles, and intercellular gaps were reduced, compared to conventionally in vitro-propagated plants. Moreover, these conditions promote morphophysiological responses and favored survival of E. elatior plants (75%) when transferred to ex vitro conditions.

Influence of seawater acidification on biochemical composition and oxidative status of green algae Ulva compressa

The sequestration of elevated atmospheric CO2 levels in seawater results in increasing acidification of oceans and it is unclear what the consequences of this will be on seaweed ecophysiology and ecological services they provide in the coastal ecosystem. In the present study, we examined the physiological and biochemical response of intertidal green seaweed Ulva compressa to elevated pCO2 induced acidification. The green seaweed was exposed to control (pH 8.1) and acidified (pH 7.7) conditions for 2 weeks following which net primary productivity, pigment content, oxidative status and antioxidant enzymes, primary and secondary metabolites, and mineral content were assessed. We observed an increase in primary productivity of the acidified samples, which was associated with increased levels of photosynthetic pigments. Consequently, primary metabolites levels were increased in the thalli grown under lowered pH conditions. There was also richness in various minerals and polyunsaturated fatty acids, indicating that the low pH elevated the nutritional quality of U. compressa. We found that low pH reduced malondialdehyde (MDA) content, suggesting reduced oxidative stress. Consistently we found reduced total antioxidant capacity and a general reduction in the majority of enzymatic and non-enzymatic antioxidants in the thalli grown under acidified conditions. Our results indicate that U. compressa will benefit from seawater acidification by improving productivity. Biochemical changes will affect its nutritional qualities, which may impact the food chain/food web under future acidified ocean conditions.

Effect of progressive drought stress on physio-biochemical responses and gene expression patterns in wheat.

The online version contains supplementary material available at 10.1007/s13205-021-02991-6.

Growth, Mineral Nutrients, Photosynthesis and Related Physiological Parameters of Citrus in Response to Nitrogen Deficiency

Limited data are available on the physiological responses of Citrus to nitrogen (N) deficiency. ‘Xuegan’ (Citrus sinensis (L.) Osbeck) and ‘Shantian pummelo’ (Citrus grandis (L.) Osbeck) seedlings were fertilized with nutrient solution at a N concentration of 0, 5, 10, 15 or 20 mM for 10 weeks. N deficiency decreased N uptake and N concentration in leaves, stems and roots and disturbed nutrient balance and homeostasis in plants, thus inhibiting plant growth, as well as reducing photosynthetic pigment levels and impairing thylakoid structure and photosynthetic electron transport chain (PETC) in leaves, hence lowering CO2 assimilation. The imbalance of nutrients intensified N deficiency’s adverse impacts on biomass, PETC, CO2 assimilation and biosynthesis of photosynthetic pigments. Citrus displayed adaptive responses to N deficiency, including (a) elevating the distributions of N and other elements in roots, as well as root dry weight (DW)/shoot DW ratio and root-surface-per-unit volume and (b) improving photosynthetic N use efficiency (PNUE). In general, N deficiency had less impact on biomass and photosynthetic pigment levels in C. grandis than in C. sinensis seedlings, demonstrating that the tolerance of C. grandis seedlings to N deficiency was slightly higher than that of C. sinensis seedlings, which might be related to the higher PNUE of the former.

Nasturtium officinale R.Br. ve Mentha aquatica L. taksonlarının farklı kurşun elementi konsantrasyonlarındaki tepkilerinin araştırılması

In this study, it was aimed to determine the morphological and physiological effects of agricultural activities and lead pollution on Nasturtium officinale and Mentha aquatica macrophytes living in Umurbey Stream (Çanakkale), and also the competition between plants in this region was investigated. Macrophytes were collected between May-June 2016 from the lower part of Gökköy Passage, which is covered with orchards on both sides of Çanakkale province, Umurbey district, Umurbey Stream. The macrophytes were left in the nutrient solution for 3 days for the adaptation process. In the first stage, the effect of lead contamination on the morphology and physiology of macrophyte species was investigated in a single culture at 1, 5 and 10 ppm Pb concentrations. Then, the competitiveness of two macrophyte species at an intermediate dose of 5 ppm Pb in a mixed culture was examined. In addition to the amount of, chlorophyll a and b, carotenoid, free proline, protein, total phenolic compound amount, adsorbed lead amount and total potassium, phosphorus, iron and magnesium amounts were examined. P, Fe, Mg, K, Pb and protein content reached the highest level at the dose of 5 ppm Pb where N. officinale was affected the most morphologically. At the same time, N officinale minimized the photosynthetic pigment and free proline levels at this dose. The dose at which M. aquatica was most affected morphologically was 10 ppm Pb dose. P, Fe, Mg and K contents of M. aquatica at that dose reached the highest value. This study proved that M. aquatica was morphologically and physiologically more resistant in two control groups where there was no lead stress and aquatic plants were grown together. Morphologically and physiologically, it has been shown that N. officinale was more combative when lead was applied as stress. With this study, it was determined that watercress is a good lead accumulator by adsorbing more than twice the lead amount absorbed by water mint.

A Consortium of Rhizosphere-Competent Actinobacteria Exhibiting Multiple Plant Growth-Promoting Traits Improves the Growth of Avicennia marina in the United Arab Emirates

Gray mangrove (Avicennia marina) is the dominant vegetation distributed along the coast of the United Arab Emirates (UAE). Despite its performance as natural coastal guardians, very little is known about the reforestation projects to increase mangrove cover over the years in the UAE and in the Arabian Gulf. Plant growth-promoting actinobacteria (PGPA) were isolated from the mangrove rhizosphere sediments found in the UAE and were evaluated for their potential to produce plant growth regulators (PGRs) and to enhance mangrove growth under seawater irrigation conditions.In vitroscreening identified nine rhizosphere-competent actinobacterial isolates, in a naturally competitive environment, of whichStreptomyces coelicoflavus(Sc) showed a high phosphorus solubilizing activity. Moreover,Streptomyces polychromogenes(Sp),Streptomyces bacillaris(Sb), andStreptomyces ferrugineus(Sf) produced auxins, polyamines (PAs), and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, respectively. Although sediment inoculation with single isolates significantly improved the dry biomass of mangrove shoots (43.2–74.0%) and roots (40.8–75.9%), the consortium of isolates (Sc/Sp/Sb/Sf) caused a greater increase in the dry weight of shoots (82.1%) and roots (81.6%) compared with seawater-irrigated plants (control). In our greenhouse experiments, the levels of photosynthetic pigments,in plantaauxins, and PAs significantly increased in plant tissues inoculated withSc/Sp/Sb/Sf; whereas ACC contents were reduced. This was also evident as the maximum velocity of rubisco carboxylation (Vcmax) increased four-fold in plants treated with the mixture of isolates over control. To the best of our knowledge, this is the first study reporting culturable halotolerant, rhizosphere-competent PGPA inhabiting salty and arid ecosystems applied individually or in combination to promote mangrove growth under harsh conditions such as those found in the Arabian coastal areas.

Comparison of selenite and selenate in alleviation of drought stress in Nicotiana tabacum L.

Exogenous selenium (Se) improves the tolerance of plants to abiotic stress. However, the effects and mechanisms of different Se species on drought stress alleviation are poorly understood. This study aims to evaluate and compare the different effects and mechanisms of sodium selenate (Na2SeO4) and sodium selenite (Na2SeO3) on the growth, photosynthesis, antioxidant system, osmotic substances and stress-responsive gene expression of Nicotiana tabacum L. under drought stress. The results revealed that drought stress could significantly inhibit growth, whereas both Na2SeO4 and Na2SeO3 could significantly facilitate the growth of N. tabacum under drought stress. However, compared to Na2SeO3, Se application as Na2SeO4 induced a significant increase in the root tip number and number of bifurcations under drought stress. Furthermore, both Na2SeO4 and Na2SeO3 displayed higher levels of photosynthetic pigments, better photosynthesis, and higher concentrations of osmotic substances, antioxidant enzymes, and stress-responsive gene (NtCDPK2, NtP5CS, NtAREB and NtLEA5) expression than drought stress alone. However, the application of Na2SeO4 showed higher expression levels of the NtP5CS and NtAREB genes than Na2SeO3. Both Na2SeO4 and Na2SeO3 alleviated many of the deleterious effects of drought in leaves, which was achieved by reducing stress-induced lipid peroxidation (MDA) and H2O2 content by enhancing the activity of antioxidant enzymes, while Na2SeO4 application showed lower H2O2 and MDA content than Na2SeO3 application. Overall, the results confirm the positive effects of Se application, especially Na2SeO4 application, which is markedly superior to Na2SeO3 in the role of resistance towards abiotic stress in N. tabacum.

The Efficiency of LED Irradiation for Cultivating High-Quality Tomato Seedlings

Light qualities are considered to affect many plant physiological processes during growth and development. To investigate how light qualities make an influence on tomato seedlings under greenhouse conditions, the growth and morphological parameters of tomato seedlings (Fortizia F1RC hybrid) were studied under three supplemental light irradiations such as light-emitting diodes with nanoparticle coating (LED 1—Red light-emitting diodes); Blue, Green, Yellow, Red light-emitting diodes (LED 2), and traditional high-pressure sodium (HPS) lamps with different photosynthetic photon flux density and the same irradiation time for 33 days. Morphological appearances of three groups of tomato seedlings were different between light treatments, that is, the plants under LED-1 and LED-2 were shorter than those under HPS, while stem diameter, leaf area, dry and fresh weights, and health indices of tomato seedlings grown under alternative light sources were higher than of those cultivated under traditional HPS lights. However, the higher plant height was in plants containing traditional high-pressure sodium lamps treatment. Photosynthetic pigments were shown to have a significant difference under respective light irradiations of LEDs. The levels of photosynthetic pigments were higher in the leaves of seedlings under LED 1 and LED 2, and lower in those that underwent HPS control treatment. Based on the data of morphological and statistical analysis, LEDs with nanoparticle coating proved to be beneficial factors for the growth of tomato seedlings under greenhouse conditions.

DASH cryptochrome 1, a UV-A receptor, balances the photosynthetic machinery of Chlamydomonas reinhardtii.

Drosophila, Arabidopsis, Synechocystis, Homo (DASH) cryptochromes belong to the cryptochrome/photolyase family and can act as DNA repair enzymes. In bacteria and fungi, they also can play regulatory roles, but in plants their biological functions remain elusive. Here, we characterize CRY-DASH1 from the green alga Chlamydomonas reinhardtii. We perform biochemical and invitro photochemical analysis. For functional characterization, a knock-out mutant of cry-dash1 is used. CRY-DASH1 protein is localized in the chloroplast and accumulates at midday. Although the photoautotrophic growth of the mutant is significantly reduced compared to the wild-type (WT), the mutant has increased levels of photosynthetic pigments and a higher maximum photochemical efficiency of photosystem II (PS II). Hyper-stacking of thylakoid membranes occurs together with an increase in proteins of the PS II reaction center, D1 and its antenna CP43, but not of their transcripts. CRY-DASH1 binds fully reduced flavin adenine dinucleotide and the antenna 5,10-methenyltetrahydrofolate, leading to an absorption peak in the UV-A range. Supplementation of white light with UV-A increases photoautotrophic growth of the WT but not of the cry-dash1 mutant. These results suggest a balancing function of CRY-DASH1 in the photosynthetic machinery and point to its role as a photoreceptor for the UV-A range separated from the absorption of photosynthetic pigments.

Antifungal activity of glyphosate against fungal blast disease on glyphosate-tolerant OsmEPSPS transgenic rice

Weeds, pests, and pathogens are among the pre-harvest constraints in rice farming across rice-growing countries. For weed management, manual weeding and herbicides are widely practiced. Among the herbicides, glyphosate [N-(phosphonomethyl) glycine] is a broad-spectrum systemic chemical extensively used in agriculture. Being a competitive structural analog to phosphoenolpyruvate, it selectively inhibits the conserved 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) enzyme required for the biosynthesis of aromatic amino acids and essential metabolites in eukaryotes and prokaryotes. In the present study, we investigated the antifungal and defense elicitor activity of glyphosate against Magnaporthe oryzae on transgenic-rice overexpressing a glyphosate-resistance OsEPSPS gene (T173I + P177S; TIPS OsmEPSPS) for blast disease management. The glyphosate foliar spray on OsmEPSPS transgenic rice lines showed both prophylactic and curative suppression of blast disease comparable to a blasticide, tricyclazole. The glyphosate displayed direct antifungal activity on Magnaporthe oryzae as well as enhanced the levels of antioxidant enzymes and photosynthetic pigments in rice. However, the genes associated with phytohormones-mediated defense (OsPAD4, OsNPR1.3, and OsFMO) and innate immunity pathway (OsCEBiP and OsCERK1) were found repressed upon glyphosate spray. Altogether, the current study is the first report highlighting the overexpression of a crop-specific TIPS mutation in conjugation with glyphosate application showing potential for blast disease management in rice cultivation.

Influence of Chloride- and Soda-Dominated Salinity on Physiological and Biochemical Aspects of Halophytes with Different Strategies of Salt Metabolism

The authors study the effect of NaCl and NaHCO3 at concentrations of 1 M on the physiological and biochemical state of Salicornia perennans and Artemisia santonica for 24 hours. In our experiment, we evaluated: the accumulation of Na in the aerial part of plants, the stress index is lipid peroxidation (LPO); the state of membranes – by the composition and content of lipids and proteins, the level of photosynthetic pigments. The euhalophyte S. perennans accumulated Na on average 30% more than the glycohalophyte A. santonica. The addition of NaCl and NaHCO3 to the root environment promoted an increase in LPO in S. perennans by 2.4 times as compared to the control. In the case of A. santonica, LPO concentration increased by 1.2 times, but only when NaHCO3 was added to the soil. In addition, NaCl and NaHCO3 negatively affected plant lipids and proteins. Thus, in S. perennans plants, NaCl contributed to a decrease in phosphlipids by 34%, and NaHCO3 in glycolipids by 22% in comparison with the control. The quantitative content of the sum of water-soluble and membrane-bound proteins in the studied plants decreased by 10–36%. Chloride and soda-dominated salinity caused a decrease in the proportion of chlorophyll a and carotenoids only in S. perennans. The authors concluded that the response of the photosynthetic system and membrane complexes to various types of salinity in euhalophyte and glycohalophyte was different.

Pigment modulation in response to irradiance intensity in the fast-growing alga Picochlorum celeri

Picochlorum celeri has among the fastest photoautotrophic growth rates (~2 h doubling time in optimal conditions) reported to date for a marine alga. This study comprehensively analyzes the levels of Picochlorum celeri photosynthetic pigments, which can reach up to ~13% of the total particulate organic carbon (POC) under light-limiting conditions. The main Picochlorum celeri pigments identified include: chlorophyll a, chlorophyll b, lutein, β-carotene, canthaxanthin, violaxanthin, neoxanthin, zeaxanthin and antheraxanthin. The ketocarotenoid canthaxanthin can accumulate up to 120 mg L−1 in Picochlorum celeri liquid culture; ~12% of it was found in an extracellular polysaccharide matrix. Using a solar-simulating automated photobioreactor, we monitor the photoacclimation of cultures maintained in unshaded conditions (<0.5 μg mL−1 of total chlorophyll) through transitions from high irradiance (1000 μmoles photosynthetically active radiation (PAR) m−2 s−1) to low irradiance (60 μmoles PAR m−2 s−1), and conversely from low to high irradiance. Canthaxanthin and zeaxanthin accumulation are among the most rapid modulation responses when cultures are shifted from low to high irradiance. The violaxanthin, antherazanthin, and zeaxanthin (VAZ) pool is ~3-fold higher in high-light cultures, suggesting that the VAZ cycle combined with a dramatic reduction in chlorophyll levels are among the major mechanisms used in Picochlorum celeri to efficiently acclimate to high-irradiance levels. Responsive pigment modulation was also observed in denser cultures (~0.65 g L−1) grown under a diel cycle (pond-mimicking conditions). This research provides unique insights into the dynamics of pigment modulation and photoacclimation in response to changing irradiance in a biotechnologically promising alga and will inform future pigment engineering strategies to further improve light capture and biomass accumulation.

A Biostimulant Based on Seaweed (Ascophyllum nodosum and Laminaria digitata) and Yeast Extracts Mitigates Water Stress Effects on Tomato (Solanum lycopersicum L.)

Water deficit is one of the most problematic stressors worldwide. In this context, the use of biostimulants represents an increasingly ecological practice aimed to improve crop tolerance and mitigate the negative effects on the productivity. Here, the effect derived from the foliar application of ERANTHIS®®, a biostimulant based on seaweed (Ascophyllum nodosum and Laminaria digitata) and yeast extracts, was tested on tomato plants grown under mild water-stress conditions. The potential stress mitigation action was evaluated by monitoring morphometric (fresh weight and dry matter content), physiological (stem water potential) and biochemical (ROS scavenger enzymes activity, proline, abscisic acid, hydrogen peroxide and photosynthetic pigment content) parameters closely related to the occurrence and response to stress at both flowering and fruit-set timing. In general, we observed that plants grown under drought conditions and treated with the biostimulant had a lower amount of ABA, and MDA and proline correlated to a lower activity of ROS scavenger enzymes compared to untreated plants. These data, together with the higher stem water potential and photosynthetic pigment levels recorded for the treated plants, suggest that ERANTHIS®® may mitigate water stress effects on tomato.

Effect of flooding and drought on the content of phenolics, sugars, photosynthetic pigments and vitamin C, and antioxidant potential of young Chinese cabbage

Due to extreme climate changes, plants are exposed to severe soil water content, i.e. flooding and drought. The aim of this study was to assess the effect of different soil water content on the nutritional potential of young Chinese cabbage (Brassica rapa ssp. pekinensis) on the level of phenolics, sugars, photosynthetic pigments and antioxidant capacity. Total phenolic acids were induced in plants grown under drought conditions. Both types of stress increased soluble sugars in Chinese cabbage but reduced total tannins. Plants grown under drought had more L-ascorbic acid than the control group; however, the concentration of ferulic acid and quercetin was reduced. On the other hand, excess of water increased the amount of sinapic and ferulic acid, main hydroxycinnamic acids in Chinese cabbage. Photosynthetic pigments were more susceptible to flooding (reduced amount) than drought, the only exception was chlorophyll b whose concentration was significantly higher in plants grown under drought. In addition, among all the measured parameters, chlorophyll b reacted most specifically against flooding (decreased) and drought (increased). Chinese cabbage grown under flooding had reduced amount of porphyrins compared to the one grown under normal and drought conditions, but showed higher antioxidant capacity (ABTS). Based on the results, the use of excess water could be considered as a possibility when growing young Chinese cabbage since it increased the concentration of antioxidants sinapic and ferulic acid and resulted in higher antioxidant capacity, recorded by ABTS assay, compared to control plants.

Response of Lawn Grasses to Salinity Stress and Protective Potassium Effect

The salinity effects on lawn grasses caused by mine salts (halite and carnallitite) due to road de-icing processes was the aim of this study. Biometric and physiological parameters were evaluated after salt dosage of 50 and 100 g m−2 applied to a lawn surface twice and four times, in weekly intervals. The alleviating effect to the salinity on the grasses from potassium enriched soil was also evaluated. Protective effect of potassium included mostly plasma membrane integrity and an increase in the level of photosynthetic pigments. This probably resulted in more efficient photosynthesis and thus increased lawn growth. Simultaneously, only a slight reduction in relative water content (RWC) was noted, so the recorded increase in proline level may indicate its participation in osmotic adjustment. Our results confirm the importance of proper, and even over-optimal, potassium fertilization of lawn grasses exposed to salinity. Moreover, it is advisable to use other fossil salts instead of halite for the de-icing of near-green areas. The mined salt carnallitite which, besides NaCl, contains about 30% of carnalite (KCl·MgCl2·6H2O) could be such a substance.